JP2891365B2 - Manufacturing method of ceramic superconductor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a superconductor, and more particularly to a method for manufacturing a ceramic-based superconductor.

[Prior art] In recent years, the development of ceramic superconductors has been progressing at a rapid pace all over the world, and this superconductor greatly exceeds the conventional maximum critical temperature of 23 K of Nb ₃ Ge, −Sr−
In addition to Cu-O-based, Y-Ba-Cu-O-based, Bi-Sr-Ca-Cu-O-based and the like, ceramics exhibiting a critical temperature of 233K or 300K or higher (hereinafter referred to as Tc) have also been reported. .

As described above, there is a possibility that the ceramic superconducting material can be used at a temperature equal to or higher than the temperature of liquid nitrogen or near room temperature. In this case, it is not necessary to use expensive liquid helium. When it is used for a machine, it has a simple structure and the efficiency of a heat engine is improved.

However, ceramics are hard and brittle, bend as now Nb-Ti system has been put to practical use and Nb ₃ Sn superconductor, or can not be coiled, to overcome this point This is the first step toward practical use.

At present, the method of manufacturing wires is to heat amorphous tapes or wires in an oxygen atmosphere. Fill the inside of an alloy tube (eg Cu-Ni alloy) with the powder of the raw material and pull both ends to form a wire or tape. There has been proposed a method of forming, a method of filling ceramic powder in a copper-based alloy tube, performing heat treatment, rolling, and the like to form a wire or tape.

However, in the above method, since extremely rapid cooling is required, there is a difficulty as a method for obtaining a practical wire rod, and in the above method, it is difficult to continuously produce a long wire rod. However, the above method has a disadvantage that the processing steps are complicated. In this case, the heat treatment for forming the ceramic superconductor is preferably performed after forming, that is, in the vicinity of the final wire diameter from the viewpoint of improving the superconducting properties. It is extremely difficult and practically impossible.

As a method for improving this point, filling ceramics in a metal tube having oxidation resistance at the firing temperature of the ceramics, hardly reacting with the ceramics, and having an oxygen permeable function has been studied.

[Problems to be Solved by the Invention] In this case, firing can be performed at the final stage after molding, but it is difficult to improve the packing density of the raw material powder, and after firing, many grain boundaries remain and shrinkage occurs. And the critical current density (hereinafter referred to as Jc) is reduced due to the problem of orientation.

The present invention has been made in order to solve the above problems, and has a high Jc which eliminates various disadvantages when using a powder material.
It is an object of the present invention to provide a method for producing a ceramic-based superconductor.

According to the present invention, a superconducting substance is directly formed on a substrate by a sputtering method, and a tape made of Ag or Invar is used as the substrate. Conventionally, a study of forming a thin film of a ceramic superconducting material on a substrate by a sputtering method has been made in a Y-Ba-Cu-O system.
These methods use a ceramic substrate such as MgO, SrTiO ₃ , ZrO ₂ or the like as a substrate, and no report has been made on the formation of a thin film on a metal substrate.

[Means for Solving the Problems] The method for producing a ceramic superconductor of the present invention comprises:
~ 3) 0.3mm thick with a coefficient of linear expansion of less than × 10 ^-5 / ℃
A ceramic superconducting material is directly applied on a tape made of the following Ag or Invar by a sputtering method.

The metal (including alloy) tape in the present invention reduces the influence of heat shock and improves the adhesion to the superconducting material.
Those having a linear expansion coefficient in the vicinity of 1.0 to 1.5 × 10 ⁻⁵ / ° C. and having oxidation resistance to heating conditions in an oxygen atmosphere of 900 ° C. or less are used.

Ag or Invar is suitable as such a metal.
Further, its thickness needs to be 0.3 mm or less in order to have flexibility.

As the above ceramic superconducting material, YBa ₂ Cu ₃ OX
And BiSrCaCu ₂ OX and the like can be mentioned as typical examples, but are not limited to these.

[Operation] In the method of the present invention, since the sputtering method is used, the firing temperature of the conventional ceramic superconductor (900 to 1
It is sufficient to heat the metal tape under a heating condition lower than 000 ° C), so that it is possible to form a wire without using a noble metal having excellent oxidation resistance as the metal tape, and it is also possible to prevent the reaction between the tape and the ceramic. . At the same time, the density of ceramics is improved, and Jc is also improved due to fewer grain boundaries.

Further, by controlling the conditions for heating the tape during sputtering, the orientation can be easily controlled, and thus Jc can be easily improved. in this case,
Since no post-deposition heat treatment is required, the manufacturing process is also simplified.

By defining the coefficient of linear expansion and the thickness of the metal tape, cracks can be prevented and the flexibility can be improved.

[Examples] Examples 1 and 2 Ag and Invar tape having a thickness of 100 µm were used as metal tapes, and YBa ₂ Cu ₃ OX was coated on the tape with a thickness of 1 µm.
It was formed in thickness. The sputtering conditions at this time are shown below.

Sputtering device: rf sputtering device 13.5MHz Target: YBa _2.0 Cu _4.0 Ox sintered body Sputtering gas: Ar / O ₂ (= 1.0) Gas pressure: 9 × 10 ^-2 Torr rf power: 100W Tape temperature: 650 ° C Deposition speed: 20Å / min The metal tape was used after cleaning the surface by chemical treatment in advance. The target was prepared by mixing powders of Y ₂ O ₃ , BaCO ₃ and CuO at a predetermined ratio, calcining at 930 ° C. for 8 hours, and then heating at 950 ° C.
A powder obtained by baking for 8 hours and pulverizing the resulting powder into a disk having an outer diameter of 80 mmφ and a thickness of 1 mm was used.

After the sputtering, it was cooled to room temperature in the air or under an oxygen atmosphere.

The electric resistance of the superconducting tape thus obtained (4
Terminal method), crystal structure (X-ray diffraction), and cross-sectional structure (scanning electron microscope).

It was confirmed that the Tc of each of the superconducting tapes obtained by the above method was about 85K and the Jc was 10,000 A / cm ² or more.

 Table 1 shows the results of observation of the film formation state.

From the above results, it is clear that, in particular, in the case of Ag and Invar tape, although the crystal grain sizes are different from each other, the adhesion of the superconducting substance is good.

FIG. 1 shows an X-ray diffraction chart of Example 1 (Ag).
The peak of the Ba-Cu-O superconducting material is shown.

Example 3 A Y-Ba-Cu-O superconducting material was applied on an invar plate having a thickness of 0.1 to 1.0 mm in the same manner as in the above embodiment, and a sample having a width of 20 mm and a length of 150 mm was collected from the plate. did. A load was applied to the sample to a span length of 100 mm and a bending amount of 20 mm, and the bending state and the surface state were observed. The results are shown in Table 2.

Comparative Examples 1-2 YBa ₂ Cu ₃ OX was formed on the tape to a thickness of 1 μm in the same manner as in Examples 1-4, except that Ta and W tapes having a thickness of 100 μm were used as metal tapes. The Tc and Jc of this superconducting tape were similar to those of Examples 1 and 2. Table 1 shows the observation results of the film formation state. It is considered that the film formation state of Ta and W is poor because these oxides are relatively stable and are easily formed at the interface with the tape. Therefore, it is necessary to select a metal tape in consideration of not only physical properties but also chemical properties.

[Effects of the Invention] As described above, according to the method for manufacturing a ceramics-based superconductor of the present invention, the influence of heat shock, a decrease in the filling rate when powder is used, generation of cracks, a decrease in orientation,
The influence of the grain boundary, the reaction between the tape and the ceramic, and the like can be prevented, and a wire having high Jc and flexibility can be manufactured by a sputtering method.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart of one embodiment of a superconductor manufactured according to the present invention.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masatada Fukushima 2-1-1, Oda Sakae, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside Showa Electric Wire & Cable Co., Ltd. (72) Keiichiro Maeda 2 Ei Oda, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture (1-1) Showa Electric Wire & Cable Co., Ltd. JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 14/00-14/58

Claims (1)

(57) [Claims] 1. A ceramic superconducting material is directly deposited on a tape made of Ag or Invar having a linear expansion coefficient of 1 × 10 ^{−5 to} 3 × 10 ⁻⁵ / ° C. and having a thickness of 0.3 mm or less by a sputtering method. A method for producing a ceramic-based superconductor.